dom/ipc/PreallocatedProcessManager.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
   5  * You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_PreallocatedProcessManager_h
   8 #define mozilla_PreallocatedProcessManager_h
   9
  10 #include "base/basictypes.h"
  11 #include "mozilla/AlreadyAddRefed.h"
  12 #include "nsStringFwd.h"
  13
  14 namespace mozilla {
  15 namespace dom {
  16 class ContentParent;
  17 }  // namespace dom
  18
  19 /**
  20  * This class manages a ContentParent that it starts up ahead of any particular
  21  * need.  You can then call Take() to get this process and use it.  Since we
  22  * already started it up, it should be ready for use faster than if you'd
  23  * created the process when you needed it.
  24  *
  25  * This class watches the dom.ipc.processPrelaunch.enabled pref.  If it changes
  26  * from false to true, it preallocates a process.  If it changes from true to
  27  * false, it kills the preallocated process, if any.
  28  *
  29  * We don't expect this pref to flip between true and false in production, but
  30  * flipping the pref is important for tests.
  31  */
  32 class PreallocatedProcessManagerImpl;
  33
  34 class PreallocatedProcessManager final {
  35   typedef mozilla::dom::ContentParent ContentParent;
  36
  37  public:
  38   static PreallocatedProcessManagerImpl* GetPPMImpl();
  39
  40   static bool Enabled();
  41
  42   /**
  43    * Before first paint we don't want to allocate any processes in the
  44    * background. To avoid that, the PreallocatedProcessManager won't start up
  45    * any processes while there is a blocker active.
  46    */
  47   static void AddBlocker(const nsACString& aRemoteType, ContentParent* aParent);
  48   static void RemoveBlocker(const nsACString& aRemoteType,
  49                             ContentParent* aParent);
  50
  51   /**
  52    * Take a preallocated process, if we have one. If we don't have a
  53    * preallocated process to return, this returns null.
  54    *
  55    * If we use a preallocated process, it will schedule the start of
  56    * another on Idle (AllocateOnIdle()).
  57    */
  58   static already_AddRefed<ContentParent> Take(const nsACString& aRemoteType);
  59
  60   /**
  61    * Note that a process was shut down, and should no longer be tracked as a
  62    * preallocated process.
  63    */
  64   static void Erase(ContentParent* aParent);
  65
  66  private:
  67   PreallocatedProcessManager();
  68   DISALLOW_EVIL_CONSTRUCTORS(PreallocatedProcessManager);
  69 };
  70
  71 }  // namespace mozilla
  72
  73 #endif  // defined mozilla_PreallocatedProcessManager_h